DE3209795A1 - METHOD FOR PRODUCING THERMOSTABLE FIBERS AND THREADS - Google Patents

Abstract

The invention relates to continuous processes for preparing dimethylformamide-insoluble acrylic filaments and fibers which incur a weight loss of at most 20, preferably 15% on being heated up to 400 DEG C., by spinning appropriate polymer solutions, treating the filament bundles obtained before the first drying or heating stage in a continuous manner with an aqueous solution containing copper(I) ions, thermally fixing the copper content, and heating the bundles to 200 DEG to 350 DEG C.

Description

HOECHST AKTIENGESELLSCHAFT HOE 82 / F 051 Dr.FK/sch

Process for the production of thermally stable fibers and threads

The invention relates to continuous process for preparing in Ν, Ν-dimethylformamide insoluble synthetic filaments and fibers of acrylonitrile polymers which have a weight loss of at most 20%, preferably 15% on heating to 400 ⁰ C.

Usual polyacrylonitrile threads and fibers have under under these conditions a weight loss of approx. 30 to 40% and largely lose their textile technology vision Properties.

So far, fibers with a similarly low weight loss could only be through a separate pre-oxidation, as they were used for production is known to be obtained from carbon fibers. These are usually very time consuming and costly Preoxidation cannot be continuously combined with the manufacturing process for the starting threads.

There has therefore been no lack of attempts, especially in recent years, to reduce the pre-oxidation time by using of heavy metal salts as catalysts. For example, the impregnation of the polyacrylonitrile threads or fibers with a copper (II) chloride solution suggested.

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Λ bur also unLur diolen Iiudi nyungcn, as sic in the JP-OS 49 035 629 are described, the pre-oxidation time is still 3 hours.

Treatment of acrylic fibers with copper (I) salts for Achievement of dyeability with acid dyes only came in the early days of acrylic fiber processing as a so-called Cupro-ion staining process used. A summary of this work is given, for example, by Rath et al.

in "Melliand Textilberic ^ + - e" .3_8 (1957), pages 431 bis and 538-542. More recently, in JP-OS 51-90387, the 'aftertreatment of molded bodies with Copper (I) salts described with the aim of catalyzing the pre-oxidation during the thermal stabilization of these products.

When reacting copper (I) salts with polymers, which contain acrylonitrile building blocks, becomes a cupro-ion complex formed with the nitrile groups of polyacrylonitrile, the subsequent reaction of copper (I) salts with shaped However, forming from polyacrylonitrile is extremely expensive and, due to the instability of the copper (I) salts in aqueous solutions, especially at elevated temperatures, cannot be regulated in a reproducible manner. Treatment of Polyacrylonitrile powders with solutions of copper (I) salts lead to products that are in the known solvents for Polyacrylonitrile are insoluble or gel-like non-spinnable masses are formed in the attempted solution. If, for example, copper (I) salts are added to a finished spinning solution, the spinning solution begins to gel and can no longer be spun without interference, while possibly containing an extrusion of copper (I) salts Spinning masses to injection molded articles is not yet hindered.

So there was still the task of making threads and fibers made of organic polymers in a simple, continuous

dier way of producing the properties of the have filaments obtained by lengthy pre-oxidation or even exceed these properties.

Surprisingly, it has been found that it is possible to produce synthetic fibers and threads insoluble in dimethylformamide from acrylonitrile polymers with increased thermal stability if the polymers, which are usually spun into strands or cables, are above 100 ° C. during their production process before the first drying or a first temperature ^treatment C continuously with an aqueous solution containing copper (I) ions, the copper content in the strands or cables is ^{fixed simultaneously or by subsequent heating to temperatures above 60, preferably above 100 0} C and the strands or cables during or after Drying to temperatures of 200 to 35O ⁰ C are heated. In this process, the copper (I) ions are absorbed within seconds and can therefore be integrated into the manufacturing process of acrylonitrile-containing threads and fibers without difficulty. It doesn't play a role. essential role whether the threads were produced by a dry or wet spinning process. The uptake of copper (I) ions naturally occurs particularly easily with wet-spun threads / it is also possible, however, to load dry-spun threads that are still solvent-containing with copper (I) ions during the washing process or after-treatment process. Depending on the desired amount of absorbed copper (I) ions, the treatment can be carried out before, during or after washing the strands or cables. The copper (I) content in the threads can of course also be influenced by the length of the exposure time and the concentration in the bath liquid.

The uptake of copper (I) ions from a bath or from a spray section from room temperature is largely reversible, that is, the copper finish can be

υ 3 / ΰ j

the following washes must be removed. For this reason it is necessary to fix the copper content in the fiber. This fixation can be achieved by a
Temperature treatment above about 6O ⁰ C, preferably occur above 85 ⁰ C or be commonly passed through a drying process, in which correspondingly high temperatures. Not only that is natural for the fixing process
applied temperature, but also the residence time of the
Threads or cables matter. While the fixation requires, for example, at 65 ⁰ C longer residence times, are at temperatures above 10ü "u for the same effect only
a minute or a few more times if necessary
Seconds required. In contrast to the inclusion of the
Copper (I) ions from aqueous solutions at room temperature

If bath temperatures from about 60 ^° C. are used, fixation of the copper (I) ions in the polymer molecule is also observed at the same time. If, for example, the copper (I) bath is kept at the boiling temperature, the copper (I) ions are absorbed and the fixation takes place at the same time. To-

Part of this process, however, is that the stability of aqueous solutions containing copper (I) ions generally decreases markedly with temperature, and the controllability of the
This usually makes the absorption of copper ions noticeably more difficult.

After such a temperature treatment or fixation, the copper (I) content can no longer be washed out, it is to assume that under these conditions the copper (I) ions complex have been built into the polyacrylonitrile.

A common procedure consists in pulling the cable or the strands through a bath containing copper (I) ions and after largely squeezing off the
excess bath liquid, for example over hot

Galettes of for example 100 ⁰ C surface temperature to
to lead. You can then do another wash, if desired
be provided to remove superficially adhering copper salts

etc. from the threads, and then a customary preparation on the threads or cables in a subsequent bath apply before they are finally dried.

However, it is also possible to treat the cables with a copper (I) ion solution immediately before drying them for the first time and to fix them with the drying process. In this case, the threads have superficially non-complexly bound copper compounds that can be detached when they come into contact with water for the first time. Instead of the use of heated godets or rolls it is also possible to perform the temperature treatment for fixing the copper content in a steam atmosphere, for example at temperatures above 95 ⁰ C or using infrared heaters or by passing through a contact heat path.

The treatment medium is in all cases an aqueous solution of copper (I) salts. To make such a Solution can be approached in different ways. The following possibilities are mentioned as examples:

The desired solution can be achieved by dissolving copper (I) salts, for example CuCl _x, in water, and because of the poor solubility of these salts it is advantageous to prepare these solutions in 20 to 50% sodium chloride solutions.

Furthermore, a copper (I) ion solution by electrolytic Reduction of copper (IT.) Solutions or by heating of copper (II) salt solutions in the presence of metallic copper are generated directly, with the copper in the form a powder is added or can be generated by electrolysis.

In addition, the solution can be prepared by mixing a copper (II) salt solution be made with a reducing agent.

_{Here, the copper salt CuSO 4} × 5 HpO has proven to be particularly favorable as the usual copper (II) salt. Of the many possible reducing agents turned out to be

AldchydsulfoxylatG and here in particular the sodium salt of hydroxymethanesulfinic acid are particularly favorable, since high copper (I) ion concentrations with good stability can be obtained with this system. The stability can also be increased by using suitable complexing agents. The required low temperatures of the aqueous solutions make a significant contribution to the stability of the copper (I) solutions. In contrast to the old cuprous ion process, in which the cooking temperature was used, in almost all cases a temperature close to room temperature is sufficient. If necessary, temperatures slightly above room temperature, that is to say for example from 25 to 30 ^° C., can be used, since here the temperature constancy of the bath can be ensured by the simplest technical means. If desired, however, it is also possible to work at higher temperatures, for example 60 to 95.degree.

Since the stability of copper (I) solutions even at room temperature is only guaranteed for shorter times, the following procedure has proven to be particularly favorable.

A copper (II) salt solution in water and an aqueous solution, which contains the reducing agent are metered separately into the bath near the inlet point of the cable and mixed in the bathroom. This ensures that fresh copper (I) solution is applied to the cable will. The cable and bath fluid move in the Direct current, excess bath liquid, which is expediently largely consumed, is in the vicinity of the Cable outlet pulled out of the tub and for example returned after refreshing.

The concentration of copper (I) ions can depending on the desired Fiber properties vary within wide limits. The copper (I) solution is made by reducing copper (II) compounds so is the reducing agent

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to use at least the stoichiometric amount. It is preferable to work with a small excess in order to avoid the presence of copper (II) salts. in the In contrast to the copper (I) compounds, the copper (II) ions can are not bound in a complex by the polymer molecules, so they are washed out in subsequent washes and pollute the wastewater. A large excess of reducing agents generally has no further advantages. Rather, there is a risk that the copper (I) compound will be further reduced to metallic copper, which then will not more can be stored in the threads or fibers. The aldehyde sulfoxylates seem to make an exception here, in which even a larger excess at room temperature does not increase the copper deposition.

For the process according to the invention, those in the art customary processes for the production of polyacrylonitrile fibers and threads are used. As mentioned above, there are particular advantages in the wet spinning process, since generally the diffusion of the copper (I) ions into the wet spun ones Threads are done more easily than with dry spun threads.

Applying the copper (I) ion solution to the cables or Strands of thread can be made by various known methods, for example by guiding the cables or Strands through a bath. However, it is also possible to apply the solution via spray sections or the like. Advantageous is the most extensive possible squeezing of the fiber cables or strands before and after treatment with the aqueous copper (I) ion solution. This ensures that the copper ions are not carried over into and

Other baths No unnecessary dilution of the copper (I) ion treatment bath remains within tolerable limits. It goes without saying that it is an advantage if measures are taken that ensure good and even penetration of a thread cable or strand in the treatment liquor. For example, cables should be as wide in the

treatment bath are performed so that a depletion of the copper ion concentration or a delayed penetration with the treatment bath inside the cable is negligible if possible.
5

As already stated above, it is necessary to fix the copper (I) ions in the thread or fiber material by means of a thermal treatment. Only after a heating to temperatures of over 60 °, preferably above about 100 ⁰ C delivers the desired Kompτ exbildung within a short .Zeitein, the copper compounds are then no longer be removed by washing from the treated Fadengut to. In a subsequent wash after the temperature treatment, the amount of copper compounds that were on the surface of the thread material and could not be fixed is of course washed off.

The acrylonitrile-containing polymers used are to be understood as meaning those polymers which are more than 50%, preferably more than 85%, are made up of acrylonitrile units. Particularly good results have been achieved with Obtained polyacrylonitriles which are composed of at least 98% acrylonitrile units. As further copolymer components for example acrylic acid, methacrylic acid and their esters and amides, vinyl acetate, Vinyl chloride, vinylidene chloride, vinylidenecyanide or other unsaturated compounds which can be copolymerized with acrylonitrile.

To ensure the required good thermal stability of the yarns produced or fibers, is after drying, where appropriate, perform together with the drying, a further temperature treatment at 200 to-35O ⁰ C, is to take place preferably between 250 and 330 ° C. It is necessary to keep the threads under tension, preferably even to subject them to a slight additional stretching. The filaments can be heated to these temperatures by known customary methods, such as

• β Ο · Λ

for example the multiple guiding over heated godets, Use of infrared radiators or guidance over a contact heat path.

As a result of this high-temperature treatment under tension, the treated filament strands or cables generally have one another discolored, they have dark brown to black shades. The thermal stability of the filaments obtained was investigated with the help of thermo-gravimetric analysis.

The thermal analyzer 2 from Firir.a Mettler Instrumente AG, Greifensee, Zurich, was used as the measuring device. The samples were heated at a heating program of 10 ° C / min and an air guide of 5 l / h to 400 ⁰ C, and then determines the weight loss. The filaments thus produced continuously show a weight loss of only a maximum of 20%, less than 15, preferably% at einezn such heating to 400 ⁰ C. It can be converted within minutes in pre-oxidized fibers or yarn strands, which are then followed by a carbonization 700 ⁰ C can be subjected.

Because of their good thermal resistance, such threads and fibers are also particularly suitable for technical applications Purposes such as, for example, as a filter material for hot gas filtration, for the production of protective clothing and the like and as reinforcing fibers or threads for inorganic and organic materials, e.g. as a substitute for asbestos, e.g. in friction linings or the like. Furthermore it is possible, by means of a further heat treatment in the de-energized state, to put the products obtained into practice to make incombustible. During this temperature treatment, the threads treated in this way generally crimp.

In the heat treatment after drying at temperature of doors 200 to 35O ⁰ C, of course, the residence time of the yarn material at these temperatures plays a part. In general, residence times of a few seconds to a few minutes are required to achieve the desired

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Effect. To achieve. In either case is the temperature treatment so short that it can be integrated into a continuous filament or fiber production process. If it is not necessary to remove the copper connections adhering to the surface of the threads or cables, it is possible to combine the copper fixation process with drying and the subsequent temperature treatment.

The following are intended to further illustrate the invention Examples serve. Unless otherwise stated, the percentages and parts are based on weight units.

example 1

A 17% solution of polyacrylonitrile in dimethylformamide was spun in a known manner by the wet spinning process. The polyacrylonitrile used consisted of 99.5% acrylonitrile units and 0.5% acrylic acid methyl ester units and had a relative viscosity of 2.9. The relative viscosity was determined on solutions containing 0 _# 5 g of polymer in 100 ml of N, N-dimethylformamide showed, measuring temperature 25 ⁰ C. The temperature of the spinning solution was 90 ⁰ C. Used was a 300-hole nozzle with a diameter of the bores of 80μπι .

This spinning solution was spun in a spinning bath consisting of 50% Ν, Ν-Dimethyt formamide (DMF) and 50% water at 50 ⁰ C and withdrawn at a rate of 7 m / min from the coagulation bath followed by a wet-stretch at 60 ⁰ C in the ratio 1: 2.31 in a bath that consisted of 60% DMF and 40% water, and then ^{washed with water at 30 0} C solvent-free. After the washing process, the sliver was squeezed off to remove most of the water and passed through a tub containing an aqueous solution of 100 g of CuSO. χ 5 H ₂ O per liter and 20 g per liter of the sodium salt of hydroxymethanesulfinic acid contained. This treatment bath also contained the necessary fiber preparation. Residence time in this bath approx. 1.5 seconds.

The treatment solution was supplemented by continuously metering an aqueous solution of 200 g / l CuSO, × 5 H ₂ O and an aqueous solution of 40 g / l of the sodium salt of hydroxymethanesulfinic acid. The two solutions were mixed shortly before entering the treatment tank.

* Formula: CH ₃ SO ₂ Na χ 2 H ₂ O

After running through the tub, the sliver was squeezed off again and then ^{dried on two heating godets at 130 0} C (contact time 7 seconds) and then on two heating godets at 17O ⁰ C (contact time 14 seconds) subjected to a drawing of 1: 1.85 and on one another godet of 250 ⁰ C (contact time 9 seconds) one

Subjected to drawing of 1: 1.61 and then brought to the winding up via a cold take-off device. The brown-black discolored threads obtained had a strength of 25 cN / dtex, an elongation of 7.8% and a girth modulus of 1000 cN / tex, the single thread denier was 3.0 dtex. The thermal stability of these fibers was measured using the Mettler thermal analyzer 2. In this case a weight loss of 12% was observed up to a heating temperature of 4 00 ⁰ C in the produced according to this example, threads. A fiber produced in this way, which, however, was not subjected to any treatment with a copper (I) salt solution, showed a weight loss of 33% according to this measuring technique.
The heating of the threads or fibers obtained to 300 ^° C. without tension for a period of 2 hours resulted in an incombustible fiber which had good crimp.

Example 2

A polymer solution as described in Example 1 was spun through a nozzle with 600 holes, hole diameter 60 μm into a precipitation bath which consisted of 61% DMF and 39% water. The temperature of the precipitation bath was 5O ⁰ C. The freshly spun filaments were drawn at a speed of 6 m / min from the coagulation bath, a wet-stretch at 98 ° C of 1: 4.86 in a bath containing 62% DMF and from 38 % Water consisted, subjected and then ^{washed with water at 80 0} C solvent-free. After the washing process, the sliver was squeezed off to remove most of the water and passed through a tub containing an aqueous solution of 75 g / l CuSO. x 5 H ₀ O and 50 g / l des

τ: £ λ

Sodium salt of hydroxymethanesulfinic acid * as well as a common fiber preparation. The solution was supplemented by continuously metering an aqueous solution of 150 g / l CuSO ₄ 5 H ₂ O with an aqueous solution of 100 g / l of the sodium salt of hydroxymethanesulfinic acid. The two solutions were mixed shortly before entering the treatment bath. The copper sulfate solution that leads to the * (formula CH ₀ SO ₀ Na χ 2 H ₀ O)

/ 5 "

Was used on strengthening, additionally contained the fiber preparation.

After passing through the bath, the sliver was again squeezed off and subsequently heated godets to 2 at 190 ⁰ C (contact time 7 seconds) and then dried

2 heating godets of 310 ⁰ C subjected to a stretching of 1: 1.54. The cable was then heated up to 2 additional godets 310 and 330 ⁰ C surface temperature, and then placed on a cold draw-off device for winding up, wherein again a drawing to 1: 1.06 was carried out. The pure contact times of the treated cord at 310 ⁰ C were 50 seconds and at 33O ⁰ C 15.7 seconds. The dunkelverfärbten individual filaments of the treated cord showed a weight loss up to 400 ⁰ C of 7%. The other technical textile data were titer 1.5 dtex
Strength: 23 cN / tex
Initial module 1160 cN / tex
Elongation 7%

All details of the initial module relate to an elongation value of 100%.

Example 3

There was conducted a spinning according to Example 2, except that the treated with the copper solution fiber cable after drying at 190 ° (contact time 11 seconds) was subjected to a further wash at 80 ⁰ C and a preparation, and then a second drying at 190 ⁰ C (Contact time 11 seconds) to be subjected.

The cable was then passed over 4 godets, which were heated to 310, 310, 310 and 330 ° surface temperature. The contact time of the cable at 310 ^° C. was 61 seconds at 330 ^° C. 18 seconds. During the high temperature treatment, the fibers were drawn at 1: 1.25. The thread material obtained was subjected to a thermogravimetric analysis and showed a weight loss on heating bit; to 400 ⁰ C of less

than 10%. The textile data found amounted to

Titer 3.3 dtex ^

Strength 30 cN / tex
Elongation 11%.
Initial module 811 cN / tex

The fibers or yarn strands obtained were after a much shorter pre-oxidation, as applied to the carbon fiber production, are subjected to a carbonization at temperatures above 700 ^0C. The pre-oxidation time for these Kaoel strands was less than 7 minutes and thus only a small fraction of the time otherwise required.

Example 4

There were tow corresponding to 3 prepared and then these samples subjected to energize a heating in an oven at 250 ⁰ C for a period of 120 minutes. Fibers with good crimp and which were incombustible were obtained. After this treatment, the fibers had the following textile values

Titer 3.5 dtex

Strength 30 cN / tex

Elongation 13%

Initial modulus 800 cN / tex.

Claims (8)

-> § - HOE 82 / F 051 Patent claims: . Process for the production of Ν, Ν-dimethylformamide 'insoluble synthetic fibers and threads from acrylonitrile polymers with increased thermal stability, characterized in that a solution of a polymer which consists of more than 50 wt .-% of acrylonitrile units, according to a known dry or Wet spinning process is spun into filament strands or tows, which during the manufacturing process, however, are ^{continuously treated with an aqueous solution containing copper (I) ions before the first drying or a temperature treatment above 100 0} C, the copper content in the strands or cables simultaneously or through a subsequent heating to temperatures above 60, preferably above 100 ⁰ C is fixed and the strands or cables are heated ^{to temperatures of 200 to 350 0 C during or after drying.} 2. The method according to claim 1, characterized in that the solution containing copper (I) ions is about room temperature having. 3. The method according to claim 1 or 2, characterized in that the temperature treatment takes place ^{during or after drying at 250 to 330 ° C.} 4. The method according to any one of the preceding claims, characterized in that the fixing of the copper content and the drying or the drying and the subsequent temperature treatment or all three Heat treatments carried out as a common process step will. 5. The method according to any one of the preceding claims, characterized in that the copper (I) ion concentration of the treatment solution 0.1 to 50 g / l, preferred HOE 82 / F051 is 0.5 to 30 g / l. > 6. The method according to any one of the preceding claims, "characterized in that the filament strands or cables after the continuous treatment with a solution containing copper (I) ions and extensive stripping and / or squeezing of the excess solution initially a temperature treatment over 60, preferably above 100 ^° C., in order to then be subjected to further washing processes, to preparation and drying with subsequent thermal treatment. 7. The method according to any one of the preceding claims, characterized in that the copper (I) ions containing Solution continuously by mixing a solution containing copper (II) ions with a reducing agent containing aqueous solution is generated or refreshed, the reducing agent at least must be added in the stoichiometric ratio. 8. The method according to claim 7, characterized in that the solution containing copper (II) ions is a solution of Copper (II) sulfate in water and containing as reducing agent Solution a solution of an aldehyde sulfoxylate, preferably the sodium salt of hydroxymethanesulfinic acid, is used in water.